.The long term goal of the proposed research program is to develop and refine a fundamentally new ultrasound imaging approach enhanced by the quantification of tissue microstructure through acoustic backscatter. The enhanced imaging technique will then be adapted for use in an in situ clinical diagnosis of solid tumors with the expectation of accurate detection and diagnosis of cancer. Use of the enhanced ultrasound imaging is medically significant because it offers a quick and noninvasive means of detecting and classifying tumor types. To accomplish the beginning stages of this long-term goal, the following specific aims are proposed: 1. Assumptions of size, shape and acoustic properties of tissue microstructures are to be tested against current correlation models using different shape factors with nonlinear frequency dependence. 2. New algorithms that account for frequency-dependent attenuation losses in tissues will be tested and incorporated into backscatter measurements for improved estimation of tissue microstructures. 3. Techniques for relating tissue structures to model parameters will be optimized for rapid estimation. 4. A control group of rats seeded with tumors will be created to build a database of tissue scattering samples. 5. Relating histological data to quantification of scattering samples will be investigated and used to test the validity of the ultrasound scattering models. 6. Several techniques for combining typical ultrasound images with the quantification of tissue microstructures will be evaluated for facilitation of clinical detection and diagnosis of disease.